Re: [PATCH v4] dmabuf: Add the capability to expose DMA-BUF stats in sysfs

[Hridya Valsaraju <hridya@google.com>]

On Thu, May 27, 2021 at 3:25 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Wed, May 26, 2021 at 02:29:45PM -0700, Hridya Valsaraju wrote:
> > On Wed, May 26, 2021 at 7:01 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> > >
> > > On Wed, May 26, 2021 at 12:40:14PM +0200, Christian König wrote:
> > > > Hi Hridya,
> > > >
> > > > Am 25.05.21 um 20:37 schrieb Hridya Valsaraju:
> > > > > This patch allows statistics to be enabled for each DMA-BUF in
> > > > > sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS.
> > > > >
> > > > > The following stats will be exposed by the interface:
> > > > >
> > > > > /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> > > > > /sys/kernel/dmabuf/buffers/<inode_number>/size
> > > > > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
> > > > > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter
> > > > >
> > > > > The inode_number is unique for each DMA-BUF and was added earlier [1]
> > > > > in order to allow userspace to track DMA-BUF usage across different
> > > > > processes.
> > > > >
> > > > > Currently, this information is exposed in
> > > > > /sys/kernel/debug/dma_buf/bufinfo.
> > > > > However, since debugfs is considered unsafe to be mounted in production,
> > > > > it is being duplicated in sysfs.
> > > > >
> > > > > Procfs also uses the proc/<pid>/fdinfo/<fd> file to expose some
> > > > > information about DMA-BUF fds. However, the existing procfs interfaces
> > > > > can only provide information about the buffers for which processes
> > > > > hold fds or have the buffers mmapped into their address space.
> > > > > The sysfs interface also exposes attachment statistics for each buffer.
> > > > >
> > > > > This information will be used to derive DMA-BUF
> > > > > per-exporter stats and per-device usage stats for Android Bug reports.
> > > > > The corresponding userspace changes can be found at [2].
> > > > > Telemetry tools will also capture this information(along with other
> > > > > memory metrics) periodically as well as on important events like a
> > > > > foreground app kill (which might have been triggered by Low Memory
> > > > > Killer). It will also contribute to provide a snapshot of the system
> > > > > memory usage on other events such as OOM kills and Application Not
> > > > > Responding events.
> > > > >
> > > > > A shell script that can be run on a classic Linux environment to read
> > > > > out the DMA-BUF statistics can be found at [3](suggested by John
> > > > > Stultz).
> > > > >
> > > > > The patch contains the following major improvements over v1:
> > > > > 1) Each attachment is represented by its own directory to allow creating
> > > > > a symlink to the importing device and to also provide room for future
> > > > > expansion.
> > > > > 2) The number of distinct mappings of each attachment is exposed in a
> > > > > separate file.
> > > > > 3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
> > > > > inorder to make the interface expandable in future.
> > > > >
> > > > > All of the improvements above are based on suggestions/feedback from
> > > > > Daniel Vetter and Christian König.
> > > > >
> > > > > [1]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1088791%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C72394dc653194a3fd3fd08d91fac2fb9%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637575646676575967%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=EJ8KluQVn8FTOYRBAYpxAaG7rua46eQpmGwI%2FxIMthQ%3D&amp;reserved=0
> > > > > [2]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fandroid-review.googlesource.com%2Fq%2Ftopic%3A%2522dmabuf-sysfs%2522&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C72394dc653194a3fd3fd08d91fac2fb9%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637575646676575967%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=4sAAqK%2F6mtSr5MWpcu2EbwOvL93UA6kMwQ2uk4fMP1g%3D&amp;reserved=0+(status:open%20OR%20status:merged)
> > > > > [3]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fandroid-review.googlesource.com%2Fc%2Fplatform%2Fsystem%2Fmemory%2Flibmeminfo%2F%2B%2F1549734&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C72394dc653194a3fd3fd08d91fac2fb9%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637575646676575967%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=hs40%2FMAnJaZQA4pkYucGqeCOGk2A9dUU%2Fj9ajqAoyFk%3D&amp;reserved=0
> > > > >
> > > > > Signed-off-by: Hridya Valsaraju <hridya@google.com>
> > > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > > ---
> > > > >
> > > > > Hi Daniel,
> > > > >
> > > > > I am sending the latest version of the DMA-BUF sysfs statistics patch to
> > > > > the list again as per your suggestion to restart the discussion on it :)
> > > > > Please do take a look and let me know your thoughts, thank you!
> > > >
> > > > Daniel and Sumit might correct me, but I think in the previous discussion we
> > > > came pretty much to the conclusion that this is not the right approach.
> >
> >
> > Sorry about the confusion Christian. I should have added a brief
> > summary of our meeting with Daniel as well to provide further context.
> >
> >
> > > >
> > > > DMA-buf is just the transport vehicle for driver allocations and as Daniel
> > > > outlined it doesn't really make sense to account on a DMA-buf level except
> > > > for debugging.
> > > >
> > > > So while this patch is technically correct it will only add another halve
> > > > backed uAPI. So question is rather what the alternative should look like?
> > >
> > > So I chatted a bit with Android folks in a quick meeting, and the rough
> > > conclusions we've had was
> > >
> > > - for per-process stats we'll look into cgroups for tracking this (because
> > >   Android will add matching cgroup for each app the want to track)
> > >
> > > - same for the tracking for OOM killer
> > >
> > > - that does leave them with a gap for shared processes, for which I agreed
> > >   that just exposing the per dma-buf info is reasonable. It's not going to
> > >   be super useful on desktop linux because the dma-buf tends to not stick
> > >   around much, but it fits fairly perfectly on Android.
> > >
> > > So yeah that's why I think this is ok to have.
> > >
> > > What's missing is explaining this properly in the commit message. The
> > > commit message explains nicely what's being added (which really should be
> > > proper uapi docs in our Documentation/ files, not hidden in a commit
> > > message where it's forgotten). But it fails to explain a bit the reasons
> > > why we need this, I think a short summary of what Android needs (in an
> > > abstract sense ie. high level semantics, not the specific implementation)
> > > and why this fits and there's nothing better is needed here I think.
> >
> >
> > Thank you Daniel, let me rewrite the commit message to explain this in
> > a better manner and send out another patch set. The patch does add the
> > ABI documentation in
> > Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers. Is the
> > suggestion to add them in a different location?
>
> Hm it's a bit sparse, and it's not nicely integrated into our .rst
> documents. E.g. we've' documented the poll() support on a dma-buf fd, see
>
> https://dri.freedesktop.org/docs/drm/driver-api/dma-buf.html#implicit-fence-poll-support
>
> That kind of overview paragraph might be nice to have.
>
> I think with the commit message polished to include all the relevant
> background, plus a short section about what's exposed in sysfs for dma-buf
> (right after the section linked above) and this is perfect. Please also
> keep Greg's r-b on the code itself so he doesn't have to look at the
> patch again.


Thank you Daniel, that makes sense! I will enhance the documentation
and commit message as per your suggestions and send out another
patchset soon.

Regards,
Hridya


>
> Cheers, Daniel
>
>
> > > > Both AMD and Intel engineers are currently discussion a fdinfo based
> > > > approach on the dri-devel mailing list.
> > > >
> > > > I strongly suggest that you join this discussion as well (and sorry I don't
> > > > have the link at hand).
> > >
> > > Yeah I think since Android keeps the dma-buf fd around anyway (by design),
> > > and since this is geared 100% for Android, implementing this exact
> > > functionality as an fdinfo on the dma-buf sounds a lot cleaner to me.
> > > Putting this in sysfs is really a bit a hack.
> >
> > The /proc/<pid>/fdinfo/<fd> interface
> > can only provide information about the buffers for which processes
> > hold fds. Hence, for the purposes of calculating per-buffer
> > statistics, parsing /proc/<pid>/fdinfo/<fd> by itself would not provide
> > a complete picture.
>
> Bummer, I had hopes, but makes sense. Please also include that in the
> commit message so that we have everything.
>
> > Thank you for the reviews and comments Greg, Christian and Daniel!
> >
> > Regards,
> > Hridya
> >
> >
> >
> > >
> > > But it is also orthogonal to our fdinfo discussion, since our fdinfo is
> > > for the drm_file, not the dma-buf fd.
> > >
> > > Except ofc I'm yet again not quite understanding what exactly Android
> > > wants/needs.
> > > -Daniel
> > >
> > > >
> > > > Regards,
> > > > Christian.
> > > >
> > > > >
> > > > > Regards,
> > > > > Hridya
> > > > >
> > > > > Changes in v4:
> > > > > -Suppress uevents from kset creation to avoid waking up uevent listeners on
> > > > > DMA-BUF export/release.
> > > > >
> > > > > Changes in v3:
> > > > > -Fix a warning reported by the kernel test robot.
> > > > >
> > > > > Changes in v2:
> > > > > -Move statistics to /sys/kernel/dmabuf/buffers in oder to allow addition
> > > > > of other DMA-BUF-related sysfs stats in future. Based on feedback from
> > > > > Daniel Vetter.
> > > > > -Each attachment has its own directory to represent attaching devices as
> > > > > symlinks and to introduce map_count as a separate file. Based on
> > > > > feedback from Daniel Vetter and Christian König. Thank you both!
> > > > > -Commit messages updated to point to userspace code in AOSP that will
> > > > > read the DMA-BUF sysfs stats.
> > > > >
> > > > >   .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  52 +++
> > > > >   drivers/dma-buf/Kconfig                       |  11 +
> > > > >   drivers/dma-buf/Makefile                      |   1 +
> > > > >   drivers/dma-buf/dma-buf-sysfs-stats.c         | 300 ++++++++++++++++++
> > > > >   drivers/dma-buf/dma-buf-sysfs-stats.h         |  62 ++++
> > > > >   drivers/dma-buf/dma-buf.c                     |  37 +++
> > > > >   include/linux/dma-buf.h                       |  20 ++
> > > > >   7 files changed, 483 insertions(+)
> > > > >   create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > > > >   create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
> > > > >   create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h
> > > > >
> > > > > diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > > > > new file mode 100644
> > > > > index 000000000000..73a8c372b0f2
> > > > > --- /dev/null
> > > > > +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > > > > @@ -0,0 +1,52 @@
> > > > > +What:              /sys/kernel/dmabuf/buffers
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       The /sys/kernel/dmabuf/buffers directory contains a
> > > > > +           snapshot of the internal state of every DMA-BUF.
> > > > > +           /sys/kernel/dmabuf/buffers/<inode_number> will contain the
> > > > > +           statistics for the DMA-BUF with the unique inode number
> > > > > +           <inode_number>
> > > > > +Users:             kernel memory tuning/debugging tools
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This file is read-only and contains the name of the exporter of
> > > > > +           the DMA-BUF.
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/size
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This file is read-only and specifies the size of the DMA-BUF in
> > > > > +           bytes.
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/attachments
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This directory will contain subdirectories representing every
> > > > > +           attachment of the DMA-BUF.
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This directory will contain information on the attaching device
> > > > > +           and the number of current distinct device mappings.
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/device
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This file is read-only and is a symlink to the attaching devices's
> > > > > +           sysfs entry.
> > > > > +
> > > > > +What:              /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/map_counter
> > > > > +Date:              May 2021
> > > > > +KernelVersion:     v5.13
> > > > > +Contact:   Hridya Valsaraju <hridya@google.com>
> > > > > +Description:       This file is read-only and contains a map_counter indicating the
> > > > > +           number of distinct device mappings of the attachment.
> > > > > diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> > > > > index 4e16c71c24b7..9561e3d2d428 100644
> > > > > --- a/drivers/dma-buf/Kconfig
> > > > > +++ b/drivers/dma-buf/Kconfig
> > > > > @@ -72,6 +72,17 @@ menuconfig DMABUF_HEAPS
> > > > >       allows userspace to allocate dma-bufs that can be shared
> > > > >       between drivers.
> > > > > +menuconfig DMABUF_SYSFS_STATS
> > > > > +   bool "DMA-BUF sysfs statistics"
> > > > > +   select DMA_SHARED_BUFFER
> > > > > +   help
> > > > > +      Choose this option to enable DMA-BUF sysfs statistics
> > > > > +      in location /sys/kernel/dmabuf/buffers.
> > > > > +
> > > > > +      /sys/kernel/dmabuf/buffers/<inode_number> will contain
> > > > > +      statistics for the DMA-BUF with the unique inode number
> > > > > +      <inode_number>.
> > > > > +
> > > > >   source "drivers/dma-buf/heaps/Kconfig"
> > > > >   endmenu
> > > > > diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> > > > > index 995e05f609ff..40d81f23cacf 100644
> > > > > --- a/drivers/dma-buf/Makefile
> > > > > +++ b/drivers/dma-buf/Makefile
> > > > > @@ -6,6 +6,7 @@ obj-$(CONFIG_DMABUF_HEAPS)  += heaps/
> > > > >   obj-$(CONFIG_SYNC_FILE)           += sync_file.o
> > > > >   obj-$(CONFIG_SW_SYNC)             += sw_sync.o sync_debug.o
> > > > >   obj-$(CONFIG_UDMABUF)             += udmabuf.o
> > > > > +obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
> > > > >   dmabuf_selftests-y := \
> > > > >     selftest.o \
> > > > > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
> > > > > new file mode 100644
> > > > > index 000000000000..45717c8108c8
> > > > > --- /dev/null
> > > > > +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> > > > > @@ -0,0 +1,300 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0-only
> > > > > +/*
> > > > > + * DMA-BUF sysfs statistics.
> > > > > + *
> > > > > + * Copyright (C) 2021 Google LLC.
> > > > > + */
> > > > > +
> > > > > +#include <linux/dma-buf.h>
> > > > > +#include <linux/dma-resv.h>
> > > > > +#include <linux/kobject.h>
> > > > > +#include <linux/printk.h>
> > > > > +#include <linux/slab.h>
> > > > > +#include <linux/sysfs.h>
> > > > > +
> > > > > +#include "dma-buf-sysfs-stats.h"
> > > > > +
> > > > > +#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
> > > > > +
> > > > > +struct dma_buf_stats_attribute {
> > > > > +   struct attribute attr;
> > > > > +   ssize_t (*show)(struct dma_buf *dmabuf,
> > > > > +                   struct dma_buf_stats_attribute *attr, char *buf);
> > > > > +};
> > > > > +#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
> > > > > +
> > > > > +static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
> > > > > +                                       struct attribute *attr,
> > > > > +                                       char *buf)
> > > > > +{
> > > > > +   struct dma_buf_stats_attribute *attribute;
> > > > > +   struct dma_buf_sysfs_entry *sysfs_entry;
> > > > > +   struct dma_buf *dmabuf;
> > > > > +
> > > > > +   attribute = to_dma_buf_stats_attr(attr);
> > > > > +   sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> > > > > +   dmabuf = sysfs_entry->dmabuf;
> > > > > +
> > > > > +   if (!dmabuf || !attribute->show)
> > > > > +           return -EIO;
> > > > > +
> > > > > +   return attribute->show(dmabuf, attribute, buf);
> > > > > +}
> > > > > +
> > > > > +static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
> > > > > +   .show = dma_buf_stats_attribute_show,
> > > > > +};
> > > > > +
> > > > > +static ssize_t exporter_name_show(struct dma_buf *dmabuf,
> > > > > +                             struct dma_buf_stats_attribute *attr,
> > > > > +                             char *buf)
> > > > > +{
> > > > > +   return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
> > > > > +}
> > > > > +
> > > > > +static ssize_t size_show(struct dma_buf *dmabuf,
> > > > > +                    struct dma_buf_stats_attribute *attr,
> > > > > +                    char *buf)
> > > > > +{
> > > > > +   return sysfs_emit(buf, "%zu\n", dmabuf->size);
> > > > > +}
> > > > > +
> > > > > +static struct dma_buf_stats_attribute exporter_name_attribute =
> > > > > +   __ATTR_RO(exporter_name);
> > > > > +static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
> > > > > +
> > > > > +static struct attribute *dma_buf_stats_default_attrs[] = {
> > > > > +   &exporter_name_attribute.attr,
> > > > > +   &size_attribute.attr,
> > > > > +   NULL,
> > > > > +};
> > > > > +ATTRIBUTE_GROUPS(dma_buf_stats_default);
> > > > > +
> > > > > +static void dma_buf_sysfs_release(struct kobject *kobj)
> > > > > +{
> > > > > +   struct dma_buf_sysfs_entry *sysfs_entry;
> > > > > +
> > > > > +   sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> > > > > +   kfree(sysfs_entry);
> > > > > +}
> > > > > +
> > > > > +static struct kobj_type dma_buf_ktype = {
> > > > > +   .sysfs_ops = &dma_buf_stats_sysfs_ops,
> > > > > +   .release = dma_buf_sysfs_release,
> > > > > +   .default_groups = dma_buf_stats_default_groups,
> > > > > +};
> > > > > +
> > > > > +#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dma_buf_attach_sysfs_entry, kobj)
> > > > > +
> > > > > +struct dma_buf_attach_stats_attribute {
> > > > > +   struct attribute attr;
> > > > > +   ssize_t (*show)(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> > > > > +                   struct dma_buf_attach_stats_attribute *attr, char *buf);
> > > > > +};
> > > > > +#define to_dma_buf_attach_stats_attr(x) container_of(x, struct dma_buf_attach_stats_attribute, attr)
> > > > > +
> > > > > +static ssize_t dma_buf_attach_stats_attribute_show(struct kobject *kobj,
> > > > > +                                              struct attribute *attr,
> > > > > +                                              char *buf)
> > > > > +{
> > > > > +   struct dma_buf_attach_stats_attribute *attribute;
> > > > > +   struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > > > > +
> > > > > +   attribute = to_dma_buf_attach_stats_attr(attr);
> > > > > +   sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> > > > > +
> > > > > +   if (!attribute->show)
> > > > > +           return -EIO;
> > > > > +
> > > > > +   return attribute->show(sysfs_entry, attribute, buf);
> > > > > +}
> > > > > +
> > > > > +static const struct sysfs_ops dma_buf_attach_stats_sysfs_ops = {
> > > > > +   .show = dma_buf_attach_stats_attribute_show,
> > > > > +};
> > > > > +
> > > > > +static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> > > > > +                           struct dma_buf_attach_stats_attribute *attr,
> > > > > +                           char *buf)
> > > > > +{
> > > > > +   return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
> > > > > +}
> > > > > +
> > > > > +static struct dma_buf_attach_stats_attribute map_counter_attribute =
> > > > > +   __ATTR_RO(map_counter);
> > > > > +
> > > > > +static struct attribute *dma_buf_attach_stats_default_attrs[] = {
> > > > > +   &map_counter_attribute.attr,
> > > > > +   NULL,
> > > > > +};
> > > > > +ATTRIBUTE_GROUPS(dma_buf_attach_stats_default);
> > > > > +
> > > > > +static void dma_buf_attach_sysfs_release(struct kobject *kobj)
> > > > > +{
> > > > > +   struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > > > > +
> > > > > +   sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> > > > > +   kfree(sysfs_entry);
> > > > > +}
> > > > > +
> > > > > +static struct kobj_type dma_buf_attach_ktype = {
> > > > > +   .sysfs_ops = &dma_buf_attach_stats_sysfs_ops,
> > > > > +   .release = dma_buf_attach_sysfs_release,
> > > > > +   .default_groups = dma_buf_attach_stats_default_groups,
> > > > > +};
> > > > > +
> > > > > +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach)
> > > > > +{
> > > > > +   struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > > > > +
> > > > > +   sysfs_entry = attach->sysfs_entry;
> > > > > +   if (!sysfs_entry)
> > > > > +           return;
> > > > > +
> > > > > +   sysfs_delete_link(&sysfs_entry->kobj, &attach->dev->kobj, "device");
> > > > > +
> > > > > +   kobject_del(&sysfs_entry->kobj);
> > > > > +   kobject_put(&sysfs_entry->kobj);
> > > > > +}
> > > > > +
> > > > > +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > > > > +                          unsigned int uid)
> > > > > +{
> > > > > +   struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > > > > +   int ret;
> > > > > +   struct dma_buf *dmabuf;
> > > > > +
> > > > > +   if (!attach)
> > > > > +           return -EINVAL;
> > > > > +
> > > > > +   dmabuf = attach->dmabuf;
> > > > > +
> > > > > +   sysfs_entry = kzalloc(sizeof(struct dma_buf_attach_sysfs_entry),
> > > > > +                         GFP_KERNEL);
> > > > > +   if (!sysfs_entry)
> > > > > +           return -ENOMEM;
> > > > > +
> > > > > +   sysfs_entry->kobj.kset = dmabuf->sysfs_entry->attach_stats_kset;
> > > > > +
> > > > > +   attach->sysfs_entry = sysfs_entry;
> > > > > +
> > > > > +   ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_ktype,
> > > > > +                              NULL, "%u", uid);
> > > > > +   if (ret)
> > > > > +           goto kobj_err;
> > > > > +
> > > > > +   ret = sysfs_create_link(&sysfs_entry->kobj, &attach->dev->kobj,
> > > > > +                           "device");
> > > > > +   if (ret)
> > > > > +           goto link_err;
> > > > > +
> > > > > +   return 0;
> > > > > +
> > > > > +link_err:
> > > > > +   kobject_del(&sysfs_entry->kobj);
> > > > > +kobj_err:
> > > > > +   kobject_put(&sysfs_entry->kobj);
> > > > > +   attach->sysfs_entry = NULL;
> > > > > +
> > > > > +   return ret;
> > > > > +}
> > > > > +void dma_buf_stats_teardown(struct dma_buf *dmabuf)
> > > > > +{
> > > > > +   struct dma_buf_sysfs_entry *sysfs_entry;
> > > > > +
> > > > > +   sysfs_entry = dmabuf->sysfs_entry;
> > > > > +   if (!sysfs_entry)
> > > > > +           return;
> > > > > +
> > > > > +   kset_unregister(sysfs_entry->attach_stats_kset);
> > > > > +   kobject_del(&sysfs_entry->kobj);
> > > > > +   kobject_put(&sysfs_entry->kobj);
> > > > > +}
> > > > > +
> > > > > +
> > > > > +/* Statistics files do not need to send uevents. */
> > > > > +static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobject *kobj)
> > > > > +{
> > > > > +   return 0;
> > > > > +}
> > > > > +
> > > > > +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
> > > > > +   .filter = dmabuf_sysfs_uevent_filter,
> > > > > +};
> > > > > +
> > > > > +static struct kset *dma_buf_stats_kset;
> > > > > +static struct kset *dma_buf_per_buffer_stats_kset;
> > > > > +int dma_buf_init_sysfs_statistics(void)
> > > > > +{
> > > > > +   dma_buf_stats_kset = kset_create_and_add("dmabuf",
> > > > > +                                            &dmabuf_sysfs_no_uevent_ops,
> > > > > +                                            kernel_kobj);
> > > > > +   if (!dma_buf_stats_kset)
> > > > > +           return -ENOMEM;
> > > > > +
> > > > > +   dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
> > > > > +                                                       &dmabuf_sysfs_no_uevent_ops,
> > > > > +                                                       &dma_buf_stats_kset->kobj);
> > > > > +   if (!dma_buf_per_buffer_stats_kset) {
> > > > > +           kset_unregister(dma_buf_stats_kset);
> > > > > +           return -ENOMEM;
> > > > > +   }
> > > > > +
> > > > > +   return 0;
> > > > > +}
> > > > > +
> > > > > +void dma_buf_uninit_sysfs_statistics(void)
> > > > > +{
> > > > > +   kset_unregister(dma_buf_per_buffer_stats_kset);
> > > > > +   kset_unregister(dma_buf_stats_kset);
> > > > > +}
> > > > > +
> > > > > +int dma_buf_stats_setup(struct dma_buf *dmabuf)
> > > > > +{
> > > > > +   struct dma_buf_sysfs_entry *sysfs_entry;
> > > > > +   int ret;
> > > > > +   struct kset *attach_stats_kset;
> > > > > +
> > > > > +   if (!dmabuf || !dmabuf->file)
> > > > > +           return -EINVAL;
> > > > > +
> > > > > +   if (!dmabuf->exp_name) {
> > > > > +           pr_err("exporter name must not be empty if stats needed\n");
> > > > > +           return -EINVAL;
> > > > > +   }
> > > > > +
> > > > > +   sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
> > > > > +   if (!sysfs_entry)
> > > > > +           return -ENOMEM;
> > > > > +
> > > > > +   sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
> > > > > +   sysfs_entry->dmabuf = dmabuf;
> > > > > +
> > > > > +   dmabuf->sysfs_entry = sysfs_entry;
> > > > > +
> > > > > +   /* create the directory for buffer stats */
> > > > > +   ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
> > > > > +                              "%lu", file_inode(dmabuf->file)->i_ino);
> > > > > +   if (ret)
> > > > > +           goto err_sysfs_dmabuf;
> > > > > +
> > > > > +   /* create the directory for attachment stats */
> > > > > +   attach_stats_kset = kset_create_and_add("attachments",
> > > > > +                                           &dmabuf_sysfs_no_uevent_ops,
> > > > > +                                           &sysfs_entry->kobj);
> > > > > +   if (!attach_stats_kset) {
> > > > > +           ret = -ENOMEM;
> > > > > +           goto err_sysfs_attach;
> > > > > +   }
> > > > > +
> > > > > +   sysfs_entry->attach_stats_kset = attach_stats_kset;
> > > > > +
> > > > > +   return 0;
> > > > > +
> > > > > +err_sysfs_attach:
> > > > > +   kobject_del(&sysfs_entry->kobj);
> > > > > +err_sysfs_dmabuf:
> > > > > +   kobject_put(&sysfs_entry->kobj);
> > > > > +   dmabuf->sysfs_entry = NULL;
> > > > > +   return ret;
> > > > > +}
> > > > > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
> > > > > new file mode 100644
> > > > > index 000000000000..5f4703249117
> > > > > --- /dev/null
> > > > > +++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
> > > > > @@ -0,0 +1,62 @@
> > > > > +/* SPDX-License-Identifier: GPL-2.0-only */
> > > > > +/*
> > > > > + * DMA-BUF sysfs statistics.
> > > > > + *
> > > > > + * Copyright (C) 2021 Google LLC.
> > > > > + */
> > > > > +
> > > > > +#ifndef _DMA_BUF_SYSFS_STATS_H
> > > > > +#define _DMA_BUF_SYSFS_STATS_H
> > > > > +
> > > > > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > > > > +
> > > > > +int dma_buf_init_sysfs_statistics(void);
> > > > > +void dma_buf_uninit_sysfs_statistics(void);
> > > > > +
> > > > > +int dma_buf_stats_setup(struct dma_buf *dmabuf);
> > > > > +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > > > > +                          unsigned int uid);
> > > > > +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> > > > > +                                                  int delta)
> > > > > +{
> > > > > +   struct dma_buf_attach_sysfs_entry *entry = attach->sysfs_entry;
> > > > > +
> > > > > +   entry->map_counter += delta;
> > > > > +}
> > > > > +void dma_buf_stats_teardown(struct dma_buf *dmabuf);
> > > > > +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach);
> > > > > +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> > > > > +{
> > > > > +   struct dma_buf_sysfs_entry *entry = dmabuf->sysfs_entry;
> > > > > +
> > > > > +   return entry->attachment_uid++;
> > > > > +}
> > > > > +#else
> > > > > +
> > > > > +static inline int dma_buf_init_sysfs_statistics(void)
> > > > > +{
> > > > > +   return 0;
> > > > > +}
> > > > > +
> > > > > +static inline void dma_buf_uninit_sysfs_statistics(void) {}
> > > > > +
> > > > > +static inline int dma_buf_stats_setup(struct dma_buf *dmabuf)
> > > > > +{
> > > > > +   return 0;
> > > > > +}
> > > > > +static inline int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > > > > +                                        unsigned int uid)
> > > > > +{
> > > > > +   return 0;
> > > > > +}
> > > > > +
> > > > > +static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
> > > > > +static inline void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach) {}
> > > > > +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> > > > > +                                                  int delta) {}
> > > > > +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> > > > > +{
> > > > > +   return 0;
> > > > > +}
> > > > > +#endif
> > > > > +#endif // _DMA_BUF_SYSFS_STATS_H
> > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > > > > index f264b70c383e..184dd7acb1ed 100644
> > > > > --- a/drivers/dma-buf/dma-buf.c
> > > > > +++ b/drivers/dma-buf/dma-buf.c
> > > > > @@ -29,6 +29,8 @@
> > > > >   #include <uapi/linux/dma-buf.h>
> > > > >   #include <uapi/linux/magic.h>
> > > > > +#include "dma-buf-sysfs-stats.h"
> > > > > +
> > > > >   static inline int is_dma_buf_file(struct file *);
> > > > >   struct dma_buf_list {
> > > > > @@ -79,6 +81,7 @@ static void dma_buf_release(struct dentry *dentry)
> > > > >     if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
> > > > >             dma_resv_fini(dmabuf->resv);
> > > > > +   dma_buf_stats_teardown(dmabuf);
> > > > >     module_put(dmabuf->owner);
> > > > >     kfree(dmabuf->name);
> > > > >     kfree(dmabuf);
> > > > > @@ -580,6 +583,10 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> > > > >     file->f_mode |= FMODE_LSEEK;
> > > > >     dmabuf->file = file;
> > > > > +   ret = dma_buf_stats_setup(dmabuf);
> > > > > +   if (ret)
> > > > > +           goto err_sysfs;
> > > > > +
> > > > >     mutex_init(&dmabuf->lock);
> > > > >     INIT_LIST_HEAD(&dmabuf->attachments);
> > > > > @@ -589,6 +596,14 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> > > > >     return dmabuf;
> > > > > +err_sysfs:
> > > > > +   /*
> > > > > +    * Set file->f_path.dentry->d_fsdata to NULL so that when
> > > > > +    * dma_buf_release() gets invoked by dentry_ops, it exits
> > > > > +    * early before calling the release() dma_buf op.
> > > > > +    */
> > > > > +   file->f_path.dentry->d_fsdata = NULL;
> > > > > +   fput(file);
> > > > >   err_dmabuf:
> > > > >     kfree(dmabuf);
> > > > >   err_module:
> > > > > @@ -723,6 +738,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > > > >   {
> > > > >     struct dma_buf_attachment *attach;
> > > > >     int ret;
> > > > > +   unsigned int attach_uid;
> > > > >     if (WARN_ON(!dmabuf || !dev))
> > > > >             return ERR_PTR(-EINVAL);
> > > > > @@ -748,8 +764,13 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > > > >     }
> > > > >     dma_resv_lock(dmabuf->resv, NULL);
> > > > >     list_add(&attach->node, &dmabuf->attachments);
> > > > > +   attach_uid = dma_buf_update_attach_uid(dmabuf);
> > > > >     dma_resv_unlock(dmabuf->resv);
> > > > > +   ret = dma_buf_attach_stats_setup(attach, attach_uid);
> > > > > +   if (ret)
> > > > > +           goto err_sysfs;
> > > > > +
> > > > >     /* When either the importer or the exporter can't handle dynamic
> > > > >      * mappings we cache the mapping here to avoid issues with the
> > > > >      * reservation object lock.
> > > > > @@ -776,6 +797,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > > > >                     dma_resv_unlock(attach->dmabuf->resv);
> > > > >             attach->sgt = sgt;
> > > > >             attach->dir = DMA_BIDIRECTIONAL;
> > > > > +           dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> > > > >     }
> > > > >     return attach;
> > > > > @@ -792,6 +814,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > > > >     if (dma_buf_is_dynamic(attach->dmabuf))
> > > > >             dma_resv_unlock(attach->dmabuf->resv);
> > > > > +err_sysfs:
> > > > >     dma_buf_detach(dmabuf, attach);
> > > > >     return ERR_PTR(ret);
> > > > >   }
> > > > > @@ -841,6 +864,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> > > > >                     dma_resv_lock(attach->dmabuf->resv, NULL);
> > > > >             __unmap_dma_buf(attach, attach->sgt, attach->dir);
> > > > > +           dma_buf_update_attachment_map_count(attach, -1 /* delta */);
> > > > >             if (dma_buf_is_dynamic(attach->dmabuf)) {
> > > > >                     dma_buf_unpin(attach);
> > > > > @@ -854,6 +878,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> > > > >     if (dmabuf->ops->detach)
> > > > >             dmabuf->ops->detach(dmabuf, attach);
> > > > > +   dma_buf_attach_stats_teardown(attach);
> > > > >     kfree(attach);
> > > > >   }
> > > > >   EXPORT_SYMBOL_GPL(dma_buf_detach);
> > > > > @@ -993,6 +1018,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> > > > >     }
> > > > >   #endif /* CONFIG_DMA_API_DEBUG */
> > > > > +   if (!IS_ERR(sg_table))
> > > > > +           dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> > > > > +
> > > > >     return sg_table;
> > > > >   }
> > > > >   EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> > > > > @@ -1030,6 +1058,8 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> > > > >     if (dma_buf_is_dynamic(attach->dmabuf) &&
> > > > >         !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
> > > > >             dma_buf_unpin(attach);
> > > > > +
> > > > > +   dma_buf_update_attachment_map_count(attach, -1 /* delta */);
> > > > >   }
> > > > >   EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
> > > > > @@ -1480,6 +1510,12 @@ static inline void dma_buf_uninit_debugfs(void)
> > > > >   static int __init dma_buf_init(void)
> > > > >   {
> > > > > +   int ret;
> > > > > +
> > > > > +   ret = dma_buf_init_sysfs_statistics();
> > > > > +   if (ret)
> > > > > +           return ret;
> > > > > +
> > > > >     dma_buf_mnt = kern_mount(&dma_buf_fs_type);
> > > > >     if (IS_ERR(dma_buf_mnt))
> > > > >             return PTR_ERR(dma_buf_mnt);
> > > > > @@ -1495,5 +1531,6 @@ static void __exit dma_buf_deinit(void)
> > > > >   {
> > > > >     dma_buf_uninit_debugfs();
> > > > >     kern_unmount(dma_buf_mnt);
> > > > > +   dma_buf_uninit_sysfs_statistics();
> > > > >   }
> > > > >   __exitcall(dma_buf_deinit);
> > > > > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > > > > index efdc56b9d95f..342585bd6dff 100644
> > > > > --- a/include/linux/dma-buf.h
> > > > > +++ b/include/linux/dma-buf.h
> > > > > @@ -295,6 +295,9 @@ struct dma_buf_ops {
> > > > >    * @poll: for userspace poll support
> > > > >    * @cb_excl: for userspace poll support
> > > > >    * @cb_shared: for userspace poll support
> > > > > + * @sysfs_entry: for exposing information about this buffer in sysfs.
> > > > > + * The attachment_uid member of @sysfs_entry is protected by dma_resv lock
> > > > > + * and is incremented on each attach.
> > > > >    *
> > > > >    * This represents a shared buffer, created by calling dma_buf_export(). The
> > > > >    * userspace representation is a normal file descriptor, which can be created by
> > > > > @@ -330,6 +333,15 @@ struct dma_buf {
> > > > >             __poll_t active;
> > > > >     } cb_excl, cb_shared;
> > > > > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > > > > +   /* for sysfs stats */
> > > > > +   struct dma_buf_sysfs_entry {
> > > > > +           struct kobject kobj;
> > > > > +           struct dma_buf *dmabuf;
> > > > > +           unsigned int attachment_uid;
> > > > > +           struct kset *attach_stats_kset;
> > > > > +   } *sysfs_entry;
> > > > > +#endif
> > > > >   };
> > > > >   /**
> > > > > @@ -379,6 +391,7 @@ struct dma_buf_attach_ops {
> > > > >    * @importer_ops: importer operations for this attachment, if provided
> > > > >    * dma_buf_map/unmap_attachment() must be called with the dma_resv lock held.
> > > > >    * @importer_priv: importer specific attachment data.
> > > > > + * @sysfs_entry: For exposing information about this attachment in sysfs.
> > > > >    *
> > > > >    * This structure holds the attachment information between the dma_buf buffer
> > > > >    * and its user device(s). The list contains one attachment struct per device
> > > > > @@ -399,6 +412,13 @@ struct dma_buf_attachment {
> > > > >     const struct dma_buf_attach_ops *importer_ops;
> > > > >     void *importer_priv;
> > > > >     void *priv;
> > > > > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > > > > +   /* for sysfs stats */
> > > > > +   struct dma_buf_attach_sysfs_entry {
> > > > > +           struct kobject kobj;
> > > > > +           unsigned int map_counter;
> > > > > +   } *sysfs_entry;
> > > > > +#endif
> > > > >   };
> > > > >   /**
> > > >
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch